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Abstract:

The invention relates to an illumination system (10, 12), to a remote
phosphor layer (30; 32, 34), to a scattering layer (32), to a luminaire
(100), to a display device (300) and to a method of at least partially
correcting a light emission characteristic of at least one light source
(22) in the illumination system. The illumination system comprises an
array of light sources (20) and a remote phosphor layer and/or a
scattering layer arranged between the array of light sources and a light
output window (40) for emitting the light from the light sources. At
least one light source of the array of light sources comprises a light
emission characteristic different from the other light sources of the
array of light sources. The luminescent material (52, 54) is distributed
across the remote phosphor layer and/or the scattering structures (52)
and/or scattering material (52) are distributed across the scattering
layer for compensating at least partially the difference in light
emission characteristic of the at least one light source.
The effect of the illumination system according to the invention is that
the deviation of the at least one light source can be compensated, and as
such, binning of light sources may be omitted.

Claims:

1. An illumination system comprising an array of light sources and a
remote phosphor layer and/or a scattering layer arranged between the
array of light sources and a light output window for emitting the light
from the light sources, at least one light source of the array of light
sources comprising a light emission characteristic different from the
other light sources of the array of light sources, the remote phosphor
layer and/or scattering layer being arranged at a distance from the array
of light sources, the remote phosphor layer comprising luminescent
material arranged for converting at least a part of the light emitted by
the light sources into light of a different color, the scattering layer
comprising scattering structures and/or scattering material arranged for
scattering at least a part of the light emitted by the light sources, the
luminescent material being distributed across the remote phosphor layer
and the scattering structures and/or scattering material being
distributed across the scattering layer for compensating at least
partially the difference in light emission characteristic of the at least
one light source.

2. Illumination system as claimed in claim 1, wherein the light emission
characteristic is selected from the group consisting of: light intensity,
light color, and angular emission profile.

3. Illumination system as claimed in claim 1, wherein the distribution of
the luminescent material comprises local variations of the luminescent
material for at least partially compensating the difference in light
emission characteristic, and/or wherein the distribution of the
scattering structures and/or scattering material comprises local
variations for at least partially compensating the difference in light
emission characteristic, the local variations comprising any of: varying
a density of the luminescent material across the remote phosphor layer,
and/or varying a density of the scattering structures and/or scattering
material across the scattering layer, varying a thickness of the
luminescent material across the remote phosphor layer, and/or varying a
thickness of the scattering structures and/or scattering material across
the scattering layer, varying a mixture of different phosphor materials
and/or scattering material in the luminescent material across the remote
phosphor layer, the luminescent material comprising a mixture of
different phosphor materials and/or scattering material, each specific
phosphor material absorbing a specific part of the light emitted by the
light sources and emitting light of a specific color, varying scattering
and/or reflection properties across the remote phosphor layer for
altering a length of an optical path through the remote phosphor layer.

4. Illumination system as claimed in claim 1, wherein a combination of
the array of light sources and the remote phosphor layer and/or
scattering layer are configured for generating a substantially uniform
light distribution across the light output window.

5. Illumination system as claimed in claim 4, wherein the remote phosphor
layer and/or the scattering layer are movable inside the illumination
system for optimizing the uniformity of the light distribution across the
light output window.

6. Illumination system as claimed in claim 1, wherein the illumination
system comprises a plurality of remote phosphor layers each arranged
between the array of light sources and the light output window, each
remote phosphor layer comprising a specific luminescent material for
absorbing a specific part of the light emitted by the light sources and
emitting light of a specific color.

7. Illumination system as claimed in claim 6, wherein the plurality of
remote phosphor layers are applied on a single carrier material.

8. Illumination system as claimed in claim 1, wherein the luminescent
material is a printable luminescent material, for generating the
distribution across the remote phosphor layer via a printing process,
and/or wherein the scattering material is a printable scattering material
for generating the distribution across the scattering layer via the
printing process.

9. Illumination system as claimed in claim 1, wherein the array of light
sources comprises an array of light emitting diodes.

10. Illumination system as claimed in claim 1, wherein the light sources
in the array of light sources emit light having a central wavelength in a
range between 400 nanometers and 490 nanometers.

11-14. (canceled)

15. Method of at least partially correcting a light emission
characteristic of at least one light source in an illumination system,
the illumination system comprising an array of light sources and a remote
phosphor layer and/or a scattering layer arranged between the array of
light sources and an light output window for emitting the light from the
light sources, the at least one light source comprising a light emission
characteristic different from the other light sources of the array of
light sources, wherein the method comprises a step of: determining a
variation of the emission characteristic across the light output window
of the illumination system before applying the remote phosphor layer
and/or a scattering layer, determining a distribution of the luminescent
material and/or scattering structures and/or scattering material required
for compensating the difference in light emission characteristic of the
at least one light source, applying the luminescent material according to
the determined distribution for generating the remote phosphor layer for
compensating at least partially the difference in light emission
characteristic, and/or applying the scattering structures and/or
scattering material according to the determined distribution for
generating the scattering layer for compensating at least partially the
difference in light emission characteristic, and applying the remote
phosphor layer and/or the scattering layer to the illumination system.

Description:

FIELD OF THE INVENTION

[0001] The invention relates to an illumination system comprising a
plurality of light emitting sources and a remote phosphor layer and/or a
scattering layer.

[0002] The invention also relates to a luminaire comprising the
illumination system, to a display device comprising the illumination
system and to a method of correcting a light emission characteristic of
at least one light source in an illumination system.

BACKGROUND OF THE INVENTION

[0003] Illumination systems comprising a plurality of light sources and a
remote phosphor arrangement are known per se. They are used, inter alia,
in a luminaire for general lighting purposes, for example, for office
lighting, for shop lighting or, for example, for in-home general lighting
purposes. These illumination systems are also used in backlighting
systems and display devices comprising backlighting systems.

[0004] A remote phosphor arrangement comprises luminescent material which
absorbs part of the light emitted by a light source of the array of light
sources and converts the absorbed light into light of a different color.
When the luminescent material is arranged at a distance from the light
source or light sources, a so called remote phosphor arrangement is
obtained. Benefits when using the remote phosphor configuration are well
known and include that the conversion efficiency and the life-time of the
luminescent material are improved and that the range of luminescent
materials to choose from is improved.

[0005] Such an illumination system is, for example, known from the patent
application US 2006/0268537 in which a phosphor film that has a
fluorescent characteristic is disclosed. In a specific embodiment of this
US application a phosphor film is disclosed which is arranged remote from
three light sources which are arranged in parallel. The phosphor material
is arranged in areas in which the concentration of phosphor particles
increased with a distance from the center of the light source. In general
a phosphor has higher wavelength conversion efficiency and a larger
number of converted light components as the irradiation light increases.
Therefore, by increasing the concentration of the phosphor in a portion
father away from the luminance center of the light source, a uniform
color distribution can be generated.

[0006] A disadvantage of the known illumination system is that the
uniformity of the illumination system may still be insufficient.

SUMMARY OF THE INVENTION

[0007] It is an object of the invention to further improve the uniformity
of the illumination system.

[0008] According to a first aspect of the invention the object is achieved
with an illumination system according to claim 1. According to a second
aspect of the invention, the object is achieved with a remote phosphor
layer as claimed in claim 11. According to a third aspect of the
invention, the object is achieved with a scattering layer as claimed in
claim 12. According to a fourth aspect of the invention, the object is
achieved with a luminaire as claimed in claim 13. According to a fifth
aspect of the invention the object is achieved with a display device as
claimed in claim 14. According to a sixth aspect of the invention the
object is achieved with a method of correcting a light emission
characteristic of at least one light source in an illumination system as
claimed in claim 15.

[0009] The illumination system according to the first aspect of the
invention comprises an array of light sources and a remote phosphor layer
and/or a scattering layer arranged between the array of light sources and
a light output window for emitting the light from the light sources,

[0010] at least one light source of the array of light sources comprising
a light emission characteristic different from the other light sources of
the array of light sources,

[0011] the remote phosphor layer and/or scattering layer being arranged at
a distance from the array of light sources, the remote phosphor layer
comprising luminescent material arranged for converting at least a part
of the light emitted by the light sources into light of a different
color, the scattering layer comprising scattering structures and/or
scattering material arranged for scattering at least a part of the light
emitted by the light sources, the luminescent material being distributed
across the remote phosphor layer and the scattering structures and/or
scattering material being distributed across the scattering layer for
compensating at least partially the difference in light emission
characteristic of the at least one light source.

[0012] Light emission characteristic comprises, for example, a color of
the light emitted or may comprise a spatial color variation of the light
source and which may be different for the at least one light source
compared to the remainder of the light sources of the illumination
system. The light emission characteristic may also, for example, comprise
an emission intensity or spatial intensity variation around the light
source and which may be different for the at least one light source
compared to the remainder of the light sources of the illumination
system.

[0013] The effect of the illumination system according to the invention is
that the specific distribution of the luminescent material across the
remote phosphor layer and/or the scattering structures and/or scattering
material across the scattering layer is used to compensate differences in
emission characteristic of the at least one light source compared to the
remainder of the light sources. This compensation results in a benefit
that any binning of light sources may be omitted and that the uniformity
of the light emitted by the light output window of the illumination
system may be improved. When an array of light sources is used, for
example, an array of light emitting diodes, the individual light sources
typically have varying light emission characteristics. Often, these
variations occur due to production variations in the production process
of the individual light sources. To improve the uniformity in light
emitting diode arrays, often binning is applied. In such arrangement, the
emission characteristic of the light emitting diodes is determined and
only light emitting diodes that have substantially identical emission
characteristics are combined in a single array. Although binning provides
relatively good uniformity of the light emitted from an array of light
sources, the binning process is relatively costly and requires good
logistics. In the illumination system according to the invention, the
illumination system comprises, next to the array of light sources, also a
remote phosphor layer comprising luminescent material and/or a scattering
layer comprising scattering structures and/or scattering material. By
adapting the distribution of the luminescent material across the remote
phosphor layer and/or of the scattering structures and/or scattering
material across the scattering layer, the emission variations due to
varying emission characteristics of at least one light source in the
array of light sources can at least partially be compensated, thus
generating a relatively high uniformity of the light emitted from the
light output window of the illumination system while omitting the need
for binning.

[0014] In the known illumination system of US 2006/0268537 an array of
three light sources are combined with a phosphor film. The concentration
of the phosphor particles in the phosphor film varies such that the
concentration of the phosphor particles increases in a portion further
away from the light source. The concentration variation pattern in the
known illumination system is identical for every light source in the
array of light sources and the concentration variation pattern is
centered on an optical axis of the light source of the known illumination
system. Although the cited variation of the concentration may enable a
relatively uniform emission of light, still uniformity variations remain
due to variations in the emission characteristic of the light sources.
Still binning seems to be required to improve the uniformity of the
emission of light from the known illumination system. Even worse: now the
binning not only includes color and/or intensity variations of the light
sources which should match within the array, but also the angular light
emission variation both in intensity and color should match for every
light source. Especially, due to the predefined concentration variation
pattern provided in the known phosphor film, any deviation from the
expected angular light emission variation of the light source in the
known illumination system would cause relatively large uniformity
variations which remain present in the known illumination system. So not
only the intensity and/or color of the light sources in the array of the
known illumination system of US 2006/0268537 should match, but the
angular light emission variation of the individual light sources should
match the expected angular light emission variation used to design the
predefined concentration variation. So by applying the predetermined
concentration variation in the phosphor film as shown in the known
illumination system of US 2006/0268537, the binning process for
generating a uniform light emission distribution becomes much more
difficult as the requirements to the light sources such that they would
match become more stringent, and thus becomes more expensive.
Furthermore, the used phosphor film is relatively expensive to produce as
the phosphor particles may not simply be applied evenly across the
phosphor film.

[0015] In the illumination system according to the invention, the remote
phosphor layer and/or the scattering layer are arranged for at least
partially compensating the difference in emission characteristic. The
remote phosphor layer comprises luminescent material arranged for
converting at least a part of the light emitted by the light sources into
light of a different color. The distribution of the luminescent material
across the remote phosphor layer is generated to at least partially
compensate the difference in light emission characteristic of the at
least one light source. The scattering layer comprises scattering
structures and/or scattering material arranged for scattering at least
part of the light emitted by the light source. The distribution of the
scattering structures and/or scattering material across the scattering
layer is generated to at least partially compensate the difference in
light emission characteristic of the at least one light source. The
remote phosphor layer and/or the scattering layer according to the
invention are optimized for a specific array of light sources and are
typically different for every array of light sources and typically also
depend on the sequence of the light sources in the array of light
sources. So, although the cost for producing the remote phosphor layer
and/or scattering layer according to the invention may be comparable to
the cost to produce the known phosphor film of US 2006/0268537, however
now, due to the remote phosphor layer and/or scattering layer according
to the invention no binning or otherwise selection of light sources is
required--making the total system cost lower--while the resulting
uniformity of the light emitted from the illumination system is much
better as the distribution of the luminescent material and/or scattering
structures and/or scattering layer is tailored to the current array of
light sources.

[0017] In an embodiment of the illumination system, the distribution of
the luminescent material comprises local variations of the luminescent
material for at least partially compensating the difference in light
emission characteristic, and/or wherein the distribution of the
scattering structures and/or scattering material comprises local
variations for at least partially compensating the difference in light
emission characteristic, the local variations comprising varying a
density of the luminescent material across the remote phosphor layer,
and/or varying a density of the scattering structures and/or scattering
material across the scattering layer. The variation of the density of the
luminescent material may be sufficient to compensate any variation in the
light emission characteristics of the at least one light source, for
example, when the light sources emit substantially blue light. In such an
embodiment the luminescent material is arranged for absorbing part of the
emitted blue light and converting the absorbed blue light to, for
example, yellow light which produces substantially white light when mixed
with the remainder of the blue light from the light source. Such an
illumination system emits substantially white light in which an angular
variation of the intensity and/or color of the emitted blue light may be
compensated by varying the density of the luminescent material across the
remote phosphor layer. Alternatively or additionally a scattering layer
may be present in which the density of the scattering structures and/or
scattering material varies across the scattering layer to alter the
emitted intensity locally. The local variations may comprise varying a
thickness of the luminescent material across the remote phosphor layer,
and/or varying a thickness of the scattering structures and/or scattering
material across the scattering layer. Again, in the previous example,
having a substantially uniform luminescent material, a thickness
variation may be used to compensate for any variation in the emission
characteristics of the at least one light source. Alternatively or
additionally a scattering layer may be present in which the thickness of
the scattering structures and/or scattering material varies to alter the
emitted intensity locally. The local variations may also comprise varying
a mixture of different phosphor materials and/or scattering material in
the luminescent material across the remote phosphor layer.

[0018] The luminescent material may be used to generate a required color
of light, for example, white light having a specific color temperature.
The scattering structures and/or scattering material may be used to
locally alter the intensity of the emitted light. In such an embodiment,
the mixture of luminescent material and/or scattering structures and/or
scattering material must be adapted to ensure that the emitted light
across the light output window comprises the required specific color
temperature and intensity distribution. Altering a density of the
scattering structures and/or scattering material cause an local altering
the emission characteristic. The local variations of the luminescent
material may comprise varying scattering and/or reflection properties
across the remote phosphor layer for altering a length of an optical path
through the remote phosphor layer. By locally adapting the optical path
through the remote phosphor layer, the extent of the light conversion can
be adapted, thus locally altering the emission characteristic.

[0019] In an embodiment of the illumination system, a combination of the
array of light sources and the remote phosphor layer and/or scattering
layer is configured for generating a substantially uniform light
distribution across the light output window. As indicated before,
generally the remote phosphor layer and/or scattering layer designed for
compensating the emission characteristic of at least one light source in
the array of light sources are specific for that particular array of
light sources and typically cannot be used for a different array of light
sources while generating good uniformity. As such, the combination of the
array of light sources and the remote phosphor layer and/or scattering
layer is chosen to generate the substantially uniform light distribution.

[0020] In an embodiment of the illumination system, the remote phosphor
layer and/or the scattering layer are movable inside the illumination
system for optimizing the uniformity of the light distribution across the
light output window. By having the remote phosphor layer and/or
scattering layer movable inside the illumination system, any inaccuracies
in the production of the distribution of the luminescent material and/or
scattering structures and/or scattering material may be compensated for.
Also the positioning of the remote phosphor layer and/or scattering layer
with respect to the array of light sources may be compensated for. For
example, when increasing the distance between the light output window and
the remote phosphor layer and/or scattering layer, any remaining
non-uniformities in the light emitted by the remote phosphor layer and/or
scattering layer may be averaged out via mixing of light before the light
is emitted via the light output window. When the illumination system is,
for example, used in a backlighting unit, the number of light sources in
the array of light sources may be relatively large. Here, the lateral
positioning of the remote phosphor layer and/or scattering layer may be
critical and thus by moving the remote phosphor layer and/or scattering
layer in lateral direction substantially parallel to the array of light
sources, an optimization of the uniformity can be achieved.

[0021] In an embodiment of the illumination system, the illumination
system comprises a plurality of remote phosphor layers, each arranged
between the array of light sources and the light output window, each
remote phosphor layer comprising a specific luminescent material for
absorbing a specific part of the light emitted by the light sources and
emitting light of a specific color. The luminescent material may, for
example, comprise three different phosphor materials, a first emitting
substantially red light, a second emitting substantially green light and
a third emitting substantially blue light. By adapting, for example, a
thickness of each of the three phosphor materials individually, local
color variations may be corrected.

[0022] In an embodiment of the illumination system, the plurality of
remote phosphor layers are applied on a single carrier material. Such an
arrangement would simplify the manufacturing of the illumination system,
since, after the generation of the plurality of remote phosphor layers on
the single carrier material, the single carrier material only needs to be
positioned inside the illumination system such that the combination of
the array of light sources and the plurality of phosphor layers generate
a relatively high uniformity across the light output window. Furthermore,
the scattering layer may also be combined on or integrated within the
single carrier material to further simplify the manufacturing of the
illumination system.

[0023] In an embodiment of the illumination system, the luminescent
material is a printable luminescent material for generating the
distribution across the remote phosphor layer via a printing process,
and/or wherein the scattering material is a printable scattering material
for generating the distribution across the scattering layer via the
printing process. A benefit of this embodiment is that it simplifies the
production of the distribution of the luminescent material across the
remote phosphor layer and of the scattering material across the
scattering layer. Any printing process will do. In production, the array
of light sources may be attached to the illumination system while the
remote phosphor layer and/or scattering layer are not present in the
illumination system. Measuring the uniformity at the light output window
of the illumination system enables to calculate the density, thickness
and/or specific mixture of luminescent material and/or scattering
material locally required. This calculated information may be converted
to data which may be used by a printing device to print the required
distribution of luminescent material and/or scattering material. For the
conversion of the measured color and intensity variation into the
required local variation of luminescent material and/or scattering
material, for example, look-up tables may be used or algorithms, loops,
modeling, etc. The determination of the required distribution of the
luminescent material and/or scattering material may be improved by
measuring the uniformity of the illumination system incorporating the
array of light sources with a reference remote phosphor layer or
reference scattering layer with spatial constant composition, and
determining the spatial deviation which requires correction.

[0024] In an embodiment of the illumination system, the array of light
sources comprises an array of light emitting diodes. In the context of
this patent application, light source may include, next to the light
emitting element, also secondary optics, such as lenses and diffusers.
These secondary optics may cause the light emission characteristic to the
different which may be compensated for by a correct distribution of the
luminescent material and/or scattering structures and/or scattering
material.

[0025] In an embodiment of the illumination system, the light sources in
the array of light sources emit light having a central wavelength in a
range between 400 nanometers and 490 nanometers. Light having a central
wavelength in a range between 400 and 490 nanometers is also known as
blue light. A benefit when using blue light as light emitted by the array
of light sources is that this light is visible to humans and thus can
directly be mixed into the output of the illumination system without
conversion. Any conversion using luminescent materials to convert light
from one color to another introduces some loss of energy due to a
Stokes-shift involved in the conversion. Using light sources emitting
blue light reduces the need to convert all light from the light sources
which increases the efficiency of the illumination system. Furthermore,
the color blue is one of the primary colors which may be used to mix with
other primary colors such as red and green or such as yellow to obtain
white light. For example, when the luminescent material absorbs part of
the blue light emitted by the light source and emit yellow light, and
when the amount of luminescent material is chosen properly so as to
convert part of the blue light and transmit the remainder of the blue
light, the light emitted from the illumination system basically may, for
example, be the color white (due to the combination of remainder of the
blue light and yellow light emitted by the further luminescent material).
A further benefit when using light sources emitting blue light is that
the use of ultraviolet light in the illumination system is omitted while
still being able to produce substantially any color of light. Often,
ultraviolet light is used in phosphor converted light sources as many
phosphor materials absorb ultraviolet light and convert this absorbed
ultraviolet light into visible light. However, ultraviolet light may be
harmful to humans and should not be emitted by the illumination system.
As such, ultraviolet filters, blocking any remaining ultraviolet light
from being emitted from the illumination system may be required when the
light sources emit ultraviolet light and can be omitted when the light
sources emit blue light. Furthermore, ultraviolet light may react with
other materials in the illumination system, such as plastics, and may
damage these other materials.

[0026] In this context, light of a specific color or specific wavelength
typically comprises light having a predefined spectrum. The predefined
spectrum may, for example, comprise a primary color having a specific
bandwidth around the specific wavelength, or may, for example, comprise a
plurality of primary colors. Light of a primary color, for example,
includes Red, Green, Blue, Yellow, Amber, and Magenta light. Light of the
specific color may also comprise mixtures of primary colors, such as Blue
and Amber, or Blue, Yellow and Red. By choosing, for example, a specific
combination of the Red, Green and Blue light substantially every color
can be generated by the illumination system, including white. Also other
combinations of primary colors may be used in the illumination system
which enables the generation of substantially every color, for example,
Red, Green, Blue, Cyan and Yellow. The number of primary colors used in
the illumination system may vary.

[0027] The method of at least partially correcting a light emission
characteristic of at least one light source in the illumination system
according to the sixth aspect of the invention comprises the steps of:

[0028] determining a variation of the emission characteristic across the
light output window of the illumination system before applying the remote
phosphor layer and/or a scattering layer,

[0029] determining a distribution of the luminescent material and/or
scattering structures and/or scattering material required for
compensating the difference in light emission characteristic of the at
least one light source,

[0030] applying the luminescent material according to the determined
distribution for generating the remote phosphor layer for compensating at
least partially the difference in light emission characteristic, and/or
applying the scattering structures and/or scattering material according
to the determined distribution for generating the scattering layer for
compensating at least partially the difference in light emission
characteristic, and

[0032] These and other aspects of the invention are apparent from and will
be elucidated with reference to the embodiments described hereinafter.

[0033] In the drawings:

[0034] FIGS. 1A, 1B, and 1C show schematic cross-sectional views and a top
view of an illumination system according to the invention,

[0035]FIG. 2 shows a top view of a remote phosphor layer and/or
scattering layer according to the invention,

[0036]FIG. 3 shows a luminaire comprising the illumination system
according to the invention, and

[0037]FIG. 4 shows a schematic cross-sectional view of a display device
according to the invention comprising the illumination system as
backlighting unit.

[0038] The figures are purely diagrammatic and not drawn to scale.
Particularly for clarity, some dimensions are exaggerated strongly.
Similar components in the figures are denoted by the same reference
numerals as much as possible.

DETAILED DESCRIPTION OF EMBODIMENTS

[0039] FIGS. 1A, 1B, and 1C show schematic cross-sectional views and a top
view of an illumination system 10, 12 according to the invention. The
illumination system 10, 12 comprises an array of light sources 20 and a
remote phosphor layer 30; 32, 34 and/or scattering layer 32 which is
arranged between the array of light sources 20 and a light output window
40. The light emitted by the illumination system 10, 12 is emitted via
the light output window 40. At least one light source 22 of the array of
light sources 20 comprises a light emission characteristic different from
the other light sources of the array of light sources 20. This different
light emission characteristic may result in the at least one light source
22 to have lower intensity compared to the other light sources of the
array 20, or which may result in a different angular light distribution
emitted by the at least one light source 22. The different light emission
characteristic may also include differences with respect to the color of
light emitted by the at least one light source 22, for example, the
central wavelength of the spectrum emitted by the at least one light
source is shifted with respect to the other light sources of the array
20, or the spectral contribution of the light emitted by the at least one
light source 22 differs compared to the spectral contribution of the
light emitted by the other light sources in the array 20. This difference
in light emission characteristics typically results in a non-uniform
illumination of the light output window 40. This non-uniformity may, for
example, be a color non-uniformity when the color of the light emitted by
the at least one light source 22 deviates from the other light sources in
the array 20, or may, for example, be an intensity non-uniformity when
the intensity and/or the angular distribution of the light emitted by the
at least one light source 22 deviates from the intensity and/or angular
distribution of the light emitted by the other light sources of the array
20.

[0040] The remote phosphor layer 30; 32, 34 is generally arranged at a
distance from the array of light sources 20 to obtain a remote phosphor
arrangement. The remote phosphor layer 30; 32, 34 comprises luminescent
material 52, 54 which converts at least a part of the light emitted by
the light sources 20, 22 into light of a different color. The luminescent
material 52, 54 is distributed across the remote phosphor layer 30; 32,
34. The distribution of the luminescent material 52, 54 is chosen such
that differences in light emission characteristic of the at least one
light source 22 is at least partially compensated.

[0041] Alternatively and/or additionally a scattering layer 32 may be
arranged between the array of light sources 20 and the light output
window 40. In the current examples, only the layer indicated with
reference number 32 is indicated as a layer comprising scattering
structures 52 and/or scattering material 52 and as such functions as a
scattering layer 32. However, also other layers indicated with reference
numbers 30 and 34 may represent scattering layers or may comprises
scattering structures 52 and/or scattering material 52. Also mixtures of
luminescent materials 52, 54 and scattering material 52 may be present in
several or a single of the layers indicated in the following embodiments.
Scattering structures 52 may be any structures present on a layer which
scatter light, for example, scratches, indentations, dots etc. Scattering
material 52 represents material which may be dispersed in a carrier
material which often is transparent material and which is able to scatter
impinging light. The carrier material may, for example, next to
scattering material 52 also comprise luminescent materials 54 dispersed
in the carrier material and as such generate a combined remote phosphor
and scattering layer. The scattering structures 52 and/or scattering
material 52 are distributed across the scattering layer 32. The
distribution of the scattering structures 52 and/or scattering material
52 is chosen such that differences in light emission characteristic of
the at least one light source 22 is at least partially compensated.

[0042] To compensate the difference in light emission characteristic, the
density of the luminescent material 52, 54 across the remote phosphor
layer 30; 32, 34 and/or of the scattering structures and/or scattering
material across the scattering layer 32 may be varied. Alternatively, the
thickness of the luminescent material 52, 54 across the remote phosphor
layer 30; 32, 34 and/or of the scattering structures and/or scattering
material across the scattering layer 32 may be varied to compensate the
difference in light emission characteristic. Varying the thickness of
luminescent material 52, 54 and/or scattering material 52 may be done by
having a luminescent material 52, 54 and/or scattering material 52 which
may be deposited or printed in small quantities, for example, using
laser-printing or ink-jet-printing processes. When, for example, the
intensity or color distribution at the light output window 40 is measured
while the remote phosphor layer 30; 32, 34 and/or scattering layer 32 are
not present, the variation due to the at least one light source 22 in the
array of light sources 20 is measured. From these measurements and from
the available luminescent materials 52, 54 and/or scattering materials 52
one can determine what variation is required of the luminescent material
52, 54 and/or scattering material 52 on the remote phosphor layer 30; 32,
34 and/or the scattering layer 32 to compensate at least partially for
this different light emission characteristic of the at least one light
source 22 in the array 20. This determination of the required variation
may be done using absorption, excitation and emission spectra of the
available luminescent materials 52, 54 or may be done using look-up
tables indicating which variation improves the uniformity and what the
effect of this variation is. Alternatively, the mixture of different
phosphor materials in the luminescent material 52, 54 may be varied
across the remote phosphor layer 30; 32, 34. Often luminescent materials
52, 54 comprise a mixture of different phosphor materials, each specific
phosphor material absorbing a specific part of the light emitted by the
light sources 20 and emitting light of a specific color. By adapting the
mixture, local variations due to changes in light emission
characteristics of the light source can thus be compensated, at least
partially.

[0043] A printing system may, for example, comprise three different
print-sources for printing three different luminescent materials 52, 54
to compensate for, for example, Red, Green and Blue variations. The
printing system may also comprise a fourth print-source providing
scattering material 52 for adapting the density of scattering material 52
across the scattering layer 32 to compensate for intensity variations.
Printing all four printing sources on a single substrate 60 may generate
a single substrate comprising both luminescent materials 52, 54 and
scattering materials 52. Alternatively, scattering structures 52 may be
pre-printed via on the substrate 60, for example, via local laser
ablation of the surface of the substrate 60, while subsequently the
luminescent materials 52, 54 are applied.

[0044] FIG. 1A shows a schematic cross-sectional view along the line AA as
shown in FIG. 1B. The illumination system 10 shown in FIG. 1A comprises
the remote phosphor layer 30 arranged at a distance from the array of
light sources 20 and arranged between the array of light sources 20 and
the light output window 40. In this cross section, one of the light
sources 22 has a different light emission characteristic compared to the
other light sources in the array 20, which is indicated with a different
grey-shade. As indicated before, the difference in the light emission
characteristic may be color, angular color distribution, intensity and
angular intensity distribution which all are indicated schematically in
FIG. 1A with the different grey-shade. The illumination system 10
typically comprises a light mixing chamber 42 in which the remote
phosphor layer 30 may be movable (not shown), for example, in a direction
perpendicular to the light output window 40. Moving the remote phosphor
layer 30 away from the light output window 40 may enhance the uniformity
at the light output window 40 as the light emitted from the remote
phosphor layer 30 is mixed in the part of the light mixing chamber 42
between the remote phosphor layer 30 and the light output window 40.
Alternatively, the remote phosphor layer 30 may be movable in a direction
parallel to the remote phosphor layer 30 to, for example, correct any
misalignment due to manufacturing tolerances of the illumination system
10.

[0045] Alternatively, as indicated earlier, the layer indicated with
reference number 30 may also comprise scattering material 52 (not shown)
or may be a scattering layer 30.

[0046] FIG. 1B shows a schematic top-view of the illumination system 10
when the remote phosphor layer 30 has been removed. In this
configuration, the variation of light intensity and/or color at the light
output window 40 may be measured which may be used to determine which
variation of the luminescent material 52, 54 and/or scattering structures
52 and/or scattering material 52 is required for at least partially
compensating the difference in light emission characteristic of the at
least one light source 22. In the embodiment shown in FIG. 1B five light
sources 22 are present having a different light emission characteristic
compared to the remainder of the light sources 20. In the schematic
arrangement shown in FIG. 1B all deviating light sources 22 are indicated
with the same grey-shade. However, the individual light emission
characteristic of these deviating light sources 22 may be different from
each other in any aspect of the light emission characteristic.

[0047] After having measured the uniformity at the light output window 40
of the current array of light sources 20, the remote phosphor layer 30
may be generated (see FIG. 2), for example, printed using well known
printing techniques such as laser-printing, ink-jet-printing or any other
printing technique. Alternatively or additionally the scattering layer 32
may be generated or scattering material 52 may be added to the remote
phosphor layer 30. For this reason, the measured differences should be
converted into digital information usable for a printer (not shown) or
usable for the chosen printing technique. Furthermore, the phosphor
suspension and/or suspension of scattering material 52 should be made
with an appropriate viscosity, particle size and stability adapted to the
chosen printing technique. The remote phosphor layer 30 may also be
generated, for example, be extrusion (not shown) of phosphor-containing
plastic material into a plate with adjustable thickness--preferably
locally.

[0048] FIG. 1C shows a schematic cross-sectional view of an alternative
embodiment of the illumination system 12 according to the invention.
Again the array of light sources 20 is present with the at least one
light source 22 having a light emission characteristic which deviates
from the remainder of the light sources in the array 20. Again the remote
phosphor layer 32, 34 is arranged between the array of light sources 20
and the light output window 40. Now, the remote phosphor layer is
constituted of different luminescent materials 52, 54 which are applied
to a carrier material 60 in separate layers 32, 34 of luminescent
material 52, 54. These discrete layers 32, 34 may be directly applied on
top of each other as shown in the schematic representation of FIG. 1C, or
may, alternatively, be applied on individual carrier materials (not
shown) which each may even, for example, be individually movable in the
illumination system 12. As can be seen in FIG. 1C the thickness of the
luminescent material 52, 54 may, for example, be adapted and may even be
arranged to vary within a single layer of luminescent material 32, 33 to
at least partially compensate the difference between the light emission
characteristics of the different light sources 20.

[0049] Alternatively and/or additionally the layer having reference number
32 may be a scattering layer 32 which comprises scattering structures 52
and/or scattering material 52. In combination with the luminescent layer
54 a compensation in both color and intensity may be obtained. As
mentioned before, the luminescent layer 34 may also comprise scattering
material 52 and the scattering layer 32 may also comprise luminescent
material 54.

[0050]FIG. 2 shows a top view of a remote phosphor layer 30 and/or
scattering layer 32 according to the invention. For reference purposes,
the location of the light sources in the array of light sources 20 is
indicated with dashed lines and the location of the at least one light
source 22 having a light emission characteristic which deviates from the
remainder of the array of light sources 20 is also indicated. As can be
seen, the luminescent material 52, 54 and/or scattering structures 52
and/or scattering material 52 vary across the remote phosphor layer 30
and/or scattering layer 32 to at least partially compensate for
differences in the light emission characteristic. These variations are
again indicated by varying shades of grey for clarity. The variations
may, however, include also color variations. The variations shown in FIG.
2 may be density variations as shown in FIG. 1A or thickness variations
as shown in FIG. 1C or a combination of the two.

[0051]FIG. 3 shows a schematic representation of a luminaire 100
comprising the illumination system 10, 12 according to the invention. A
luminaire 100 is a complete lighting unit, for example, used in offices,
shops, at home, or, for example, used as lighting unit for street-lights.
The color rendering index should preferably be as high as possible such
that the illumination of an object (not shown) by the luminaire 100
results in a true reproduction of the color of the object. This high
color rendering index can be obtained by using, for example, a broad
mixture of different luminescent materials 52, 54, together emitting
light substantially covering the full visible electro-magnetic spectrum.

[0052]FIG. 4 shows a schematic representation of display device 300
comprising the illumination system 10, 12 according to the invention. The
display device 300 typically comprises a non-emissive display 310, such
as an array of liquid crystal cells which, by varying the transmission of
cells in the array of liquid crystal cells is able to create an image on
the display 300. The illumination system 10, 12 is part of a backlighting
unit 200.

[0053] It should be noted that the above-mentioned embodiments illustrate
rather than limit the invention, and that those skilled in the art will
be able to design many alternative embodiments without departing from the
scope of the appended claims.

[0054] In the claims, any reference signs placed between parentheses shall
not be construed as limiting the claim. Use of the verb "comprise" and
its conjugations does not exclude the presence of elements or steps other
than those stated in a claim. The article "a" or "an" preceding an
element does not exclude the presence of a plurality of such elements.
The invention may be implemented by means of hardware comprising several
distinct elements. In the device claim enumerating several means, several
of these means may be embodied by one and the same item of hardware. The
mere fact that certain measures are recited in mutually different
dependent claims does not indicate that a combination of these measures
cannot be used to advantage.

Patent applications by Gerardus Arnoldus Rita Van Dijk, Eindhoven NL

Patent applications by Martinus Petrus Joseph Peeters, Eindhoven NL

Patent applications by Rene Theodorus Wegh, Eindhoven NL

Patent applications by KONINKLIJKE PHILIPS ELECTRONICS N.V.

Patent applications in class LIGHT SOURCE OR LIGHT SOURCE SUPPORT AND LUMINESCENT MATERIAL

Patent applications in all subclasses LIGHT SOURCE OR LIGHT SOURCE SUPPORT AND LUMINESCENT MATERIAL